Add Icon name props for date & time pickers

I am using Feather Icons as described in the `react-native-paper` docs
https://callstack.github.io/react-native-paper/icons.html

This gives warning for icon names `pencil`, `close` and other icons show up as `?` as they are not included in Feather icon set
Therefore, there is a need to have icon name props, so that, these icons could be changed with the Icon set being used.